BACKGROUND: Type 2 diabetes Mellitus (T2DM) is associated with cardiac autonomic dysfunction, which is an independent predictor of mortality in chronic diseases. However, whether the coexistence of systemic arterial hypertension (HTN) with DMT2 alters cardiac autonomic modulation remains unknown. OBJECTIVE: To evaluate the influence of HTN on cardiac autonomic modulation and cardiorespiratory fitness in subjects with DMT2. METHODS: 60 patients of both genders were evaluated and allocated to two groups: DMT2 patients (n = 32; 51 +/- 7.5 years old) and DMT2 + HTN patients (n = 28; 51 +/- 6.9 years old). RR intervals were obtained during rest in supine position. Linear and nonlinear indices of heart rate variability (HRV) were computed using Kubios HRV software. Pulmonary gas exchange was measured breath-by-breath, using a portable telemetric system during maximal incremental exercise testing on a cycle ergometer. Statistical analysis included Shapiro-Wilk test followed by Student\'s t Test, Pearson correlation and linear regression. RESULTS: We found that patients in the DMT2+HTN group showed lower values of mean RR intervals (801.1 vs 871.5 ms), Shannon entropy (3 vs 3.2) and fractal dimension SD 1 (9.5 vs 14.5), when contrasted with patients in the DMT2 group. Negative correlations were found between some HRV nonlinear indices and exercise capacity indices. CONCLUSION: HTN negatively affects the cardiac autonomic function in diabetic patients, who are already prone to develop autonomic dysfunction. Strategies are need to improve cardiac autonomic functionality in this population.